Central Valley Rice Fields Successfully Used For Fattening Fish

WOODLAND (CBS/AP) — Alongside a flooded field of rice stubble, Jacob Katz dipped a fish net into turbid water and came up with a half dozen or so silvery juvenile salmon.

After a century of watching rivers held back by levees and California wetlands developed into farm fields, conservation groups are having some success reversing environmental consequences—at least when it comes to sensitive salmon. And in a state where farmers and environmentalists fight constantly over scarce water, finding a way to use the same supply for two purposes could be game-changing.

In February, researchers released 50,000 chinook salmon juveniles into a flooded 20-acre test field lined with canals and levees. On Wednesday, the last of those fish made their way down the Tule Canal toward Northern California’s Sacramento River and toward the ocean.

Famers and biologists collaborated to place young salmon in flooded rice fields to mimic the vast marshlands that originally lined the rivers of the Central Valley, where the fish thrived in their natural habitat. The Sacramento River used to spill its banks into rich tule marshes that were five miles wide in places, but it has since been channeled.

“When I look at the fish in the marsh, I say almost glibly that it’s almost as if they evolved there, which of course they did,” said Katz, a salmon researcher with California Trout.

“We’ve only recently come to understand that marsh was really, really valuable habitat,” said Katz. “Our system of dams and steep levees was built when very little was known about biology and very little consideration was given.”

The experiment took place in the Yolo Bypass northwest of Sacramento, a flood plain now home to thousands of acres of rice fields. In wet years, the bypass is a natural haven for salmon because the fish have a steady supply of insects and are shielded from larger predators. But most of the time, it’s not flooded long enough to benefit the salmon, so researchers worked with farmers for the past two years to find the right balance.

The participants include California Trout, a nonprofit devoted to protecting cold-water fish species; University of California, Davis; the California Department of Water Resources; and John Brennan of the Knaggs Ranch, one of the participating farms.

The researchers found that over six weeks, the test fish fattened seven times faster and had superior survival rates than their kin left to mature in the harsher deep river channel. The marshland fish grew from 55 millimeters to an average of 90 millimeters in that time.

In comparison, fish in the river grew from 38 millimeters to 44 millimeters over the same length of time. Part of that difference was from the fish’s calorie-burning movement as they avoid predators and fight the current. The river fish also are washed out to sea at an earlier stage.

“Historically, those small fish would have been swept into flood plains and would have spent a month or two getting large and robust,” Katz said.

Generally about 5 percent of river salmon make it to the ocean, but these researchers are betting that larger, healthier juveniles will more easily avoid predators, thrive in the ocean and return to spawn. About 60 from the experiment were tagged to track progress and to compare their success to a control group released from hatcheries.

Federal and state governments have built hatcheries and gravel beds to encourage spawning, but research shows that an important part of the process has been missing.

“Everyone used to think that the key to salmon success was sparkling water and gravel beds in the mountains,” said Katz. “But this is where they packed their lunch for the trip out to sea

The state’s rice paddies, which produce much of the sushi rice consumed in the U.S., take up more than a half million acres in the Sacramento Valley.

As Katz watched flood plain-fattened fish begin the months-long swim that will take them out of the Golden Gate, he considered whether salmon raised in the paddies might end up inside a seaweed wrap with the rice grown there.

“Wait three years and ask me again,” he said.

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